Traditionally flexible pipe is utilised to transport production fluids, such as oil and/or gas and/or water, from one location to another. Flexible pipe is particularly useful in connecting a sub-sea location (which may be deep underwater, say 1000 meters or more) to a sea level location. The pipe may have an internal diameter of typically up to around 0.6 meters. Flexible pipe is generally formed as an assembly of a flexible pipe body and one or more end fittings. The pipe body is typically formed as a combination of layered materials that form a pressure-containing conduit. The pipe structure allows large deflections without causing bending stresses that impair the pipe's functionality over its lifetime. The pipe body is generally built up as a combined structure including metallic and polymer layers.
In many known flexible pipe designs the pipe body includes one or more pressure armour layers. The primary load on such layers is formed from radial forces. Pressure armour layers often have a specific cross section profile to interlock so as to be able to maintain and absorb radial forces resulting from outer or inner pressure on the pipe. The cross sectional profile of the wound wires which thus prevent the pipe from collapsing or bursting as a result of pressure are sometimes called pressure-resistant profiles. When pressure armour layers are formed from helically wound wired forming hoop components, the radial forces from outer or inner pressure on the pipe cause the hoop components to expand or contract, putting a tensile load on the wires.
In many known flexible pipe designs the pipe body includes one or more tensile armour layers. The primary loading on such a layer is tension. In high pressure applications, such as in deep and ultra deep water environments, the tensile armour layer experiences high tension loads from a combination of the internal pressure end cap load and the self-supported weight of the flexible pipe. This can cause failure in the flexible pipe since such conditions are experienced over prolonged periods of time.
Unbonded flexible pipe has been used for deep water (less than 3,300 feet (1,005.84 meters)) and ultra deep water (greater than 3,300 feet) developments. It is the increasing demand for oil which is causing exploration to occur at greater and greater depths where environmental factors are more extreme. For example in such deep and ultra-deep water environments ocean floor temperature increases the risk of production fluids cooling to a temperature that may lead to pipe blockage. Increased depths also increase the pressure associated with the environment in which the flexible pipe must operate. As a result the need for high levels of performance from the armour layers of the flexible pipe body is increased.
It will be appreciated that harsh environmental conditions are present at such operating depths under the sea, including not only high pressures and strong tidal movement but also man made conditions such as collision with passing vehicles and so on.
Flexible pipe may also be used for shallow water applications (for example less than around 500 meters depth) or even for shore (overland) applications.
For any depth of use, there is an increasing desire for the continual monitoring of various parameters of flexible pipes, such as strain, temperature and acoustics, to help detect structural failures in the pipe. Such structural failure could be leakage, wire breakage, over-bending in the pipe (i.e. bending past the maximum allowable amount before which damage will occur), and interaction between the pipe and external environment such as collisions with other objects, for example.
One way which has been suggested for monitoring parameters associated with such structures is the use of an optical fibre system. As a method of monitoring strain, temperature and acoustics in flexible pipe, bare fibres and/or fibres in metal tubes (FIMT) within a protective conduit have been incorporated along the length of the pipe structure and connected to an interrogating device external of the pipe. The fibre is used as an optical fibre for transmitting light and is generally made of glass. The optical fibres can be used as strain gauges, temperature gauges, temperature indicators and strain measurements can be made which are either localised, distributed or semi-distributed depending upon the manner in which the optical fibre is interrogated and regions/sensors in the optical fibre are arranged. The fibres may include Bragg Gratings whereby differential diffraction of light passing down the fibre is used to measure the necessary parameter. Output readings can be analysed to determine the conditions of the pipe over a time period and corrective action can be taken accordingly. WO2009/068907 discloses a way in which an optical fibre can be wrapped around a flexible pipe and certain measurements taken from which parameters associated with the pipe can be determined.
Strain can be monitored by including a FIMT that is bonded to the conduit. Temperature can be monitored by including a FIMT that is not bonded to the inside of the conduit, and is therefore able to record temperature independently to strain. Fibres can be configured in a similar manner to monitor acoustic conditions.
Assembling the FIMT, and their eventual removal from the wire at the end fitting stage to enable their connection to the interrogating device, are the challenges faced with the known methods. In terms of preparation, finding an appropriate location within the flexible pipe, and the manufacturing technique itself may be problematic. At pipe completion when the end fitting is assembled, the FIMT must be separated to facilitate its connection to an external device. If the FIMT is bonded into an armour wire, for example, removing it from the wire is difficult and can induce unnecessary stress in the material. Similar challenges may arise with other types of sensing device, such as electrical cables, and the like.